Chapter 1: Superconducting Devices for Quantum Computation

James F. Annett, Balazs L. Gyorffy, Timothy P. Spiller

Zhigang Zhang, Goong Chen

B. L. T. Plourde, Timothy L. Robertson, Antonio García Martínez +5 more

Siyuan Han

This chapter focuses on the application of Nb Josephson junctions (JJs) in quantum annealing (QA). It begins with a brief introduction to diffident strategies for implementing quantum computation (QC) with an emphasis on quantum annealing. The chapter presents the basic physics of the simplest superconducting flux qubit: radio frequency superconducting quantum interference devices (RF-SQUID). It gives a brief description on the design and realization of couplers, and control and measurement circuitry using Nb Josephson junctions. The chapter describes a scalable architecture upon which quantum annealing processors consisting up to 1024 superconducting flux qubits made of more than 104 Nb Josephson junctions. It discusses evidence on whether D-Wave 2X, which is the latest quantum annealing processor available, works as expected. The chapter also focuses on the physics and application of RF-SQUID flux qubits because the fundamental building blocks of the most advanced quantum annealers demonstrated so far are variations of superconducting flux qubits with one Josephson junction, a.k.a. the RF-SQUID.

Yoav Koral, Rajkumar Sokkalingam, S. E. Schacham

This chapter explores the evolution of superconducting qubits from traditional superconductors, tracing the scientific and technological milestones that have led to their central role in quantum computing. Beginning with an overview of superconductivity, the Josephson effect, qubits, and their types, the chapter highlights superconducting qubits with their theoretical implementation. It then transitions to the development of modern qubit architectures – charge, flux, and transmon qubits – emphasizing advances in material purity, fabrication, and coherence enhancement. Special focus is given to a short description of fabricating granular aluminum qubits for quantum engineering applications. The chapter concludes with current challenges, including decoherence mitigation, material scalability, and integration with hybrid quantum systems. This work aims to provide readers with a comprehensive understanding of the journey from conventional superconductors to quantum information devices.